1. Field of the Invention
The present invention relates to a liquid crystal display device which can be used as a display device in television sets, computers, word processors, OA (Office Automation) apparatuses, and the like.
2. Description of the Related Art
FIG. 20 shows an exemplary active matrix substrate of a liquid crystal display device.
The active matrix substrate includes thin film transistors (hereinafter referred to also as "TFTs") 2 as switching elements and pixel capacitors 1. The TFTs 2 and the pixel capacitors 1 are provided on the substrate so as to be arranged in a matrix. A gate electrode of the TFT 2 is connected to a gate line 3 as a scanning line, through which a scanning signal for driving the TFT 2 is input. A source electrode of the TFT 2 is connected to a source line 5 as a signal line, through which a video signal or the like as a display signal is input. The gate lines 3 and the source lines 5 are provided so as to cross each other. A drain electrode of the TFT 2 is connected to one terminal of a pixel electrode and to one terminal of the pixel capacitor 1. The other terminal of each pixel capacitor 1 is connected to a pixel capacitor line 4.
The active matrix substrate is attached to a counter substrate, on which a counter electrode is provided, with a liquid crystal layer interposed between the substrates, thereby forming a liquid crystal display device. The pixel capacitor line 4 is connected to the counter electrode on the counter substrate.
The most typical way to conduct a color display with such a liquid crystal display device is to provide a color filter on the counter substrate. The color filter includes a plurality of colored portions of three colors: R (Red), G (Green) and B (Blue). A counter substrate including such a color filter is called a "color filter substrate". Typically, a black matrix is provided on the color filter substrate to avoid a color mixture phenomenon or light leakage.
The black matrix is provided so as to cover boundaries between pixels, thereby blocking light leaking through the boundaries between pixels of the liquid crystal layer, across which no voltage is applied. The black matrix also covers the periphery of the display region, thereby also blocking light leaking through the peripheral region. Moreover, the black matrix is also present above the TFTs, thereby blocking ambient light which would otherwise be directly incident upon the TFTs and adversely affect the display characteristics of the device considerably.
FIG. 21 shows a configuration of a conventional liquid crystal display device. The conventional liquid crystal display device includes the active matrix substrate 10a having a configuration as shown in FIG. 20. The active matrix substrate 10a is attached to the color filter substrate 10b, on which the black matrix 6 is provided. The liquid crystal display device is provided with the pixel electrodes (not shown) formed in the display region 7 on the active matrix substrate 10a. The gate lines 3 and the source lines 5 are provided on the active matrix substrate 10a so that they run in the vicinity of the pixel electrodes while crossing each other. The lines 3 and 5 both extend outwardly beyond the peripheral region 8 to respective input terminals 3a and 5a which are provided in a terminal region 9 outside the peripheral region 8. The scanning signal is input to the gate lines 3 via the input terminal 3a, and the video signal is input to the source lines 5 via the input terminal 5a. On the other side, the color filter (not shown) is provided in the display region 7 on the color filter substrate 10b so as to face the pixel electrodes on the active matrix substrate 10a. The black matrix 6 is provided so as to cover the peripheral region 8, where the color filter is not present, thereby blocking light leaking through the peripheral region 8. It should be noted that, although the black matrix is also provided in the display region 7 as described above, it is not shown in FIG. 21.
As described above, in the conventional liquid crystal display device, the color filter substrate 10b is provided with the black matrix 6 as well as the color filter which includes the colored portions of three colors: R, G and B. The black matrix 6 is usually formed by patterning a metal layer. Eliminating the formation process for the black matrix 6 is a very effective way to reduce the manufacturing cost of the liquid crystal display device. Accordingly, there has been a demand for developing a liquid crystal display device in which the black matrix 6 does not have to be provided on the color filter substrate 10b. In such a case, however, it is necessary to ensure that ambient light does not considerably influence the display characteristics even if the black matrix 6 is not provided on the color filter substrate 10b. Moreover, it is also necessary to block light leaking through the peripheral region or through the portions of the liquid crystal layer corresponding to the boundaries between pixels, across which no voltage is applied. For example, leakage of light from a backlight through the peripheral region detracts from display quality, and is particularly problematic when conducting a black display. Therefore, it is necessary to block light from the backlight. Furthermore, a viewer usually views the liquid crystal display device from the color filter substrate side. When a sealing resin or the like, used in the peripheral region for the attachment of the substrates, is visible to the viewer, the display quality is detracted. Therefore, it is desirable to make the sealing resin or the like invisible from the viewer.